Our long-term objective is to identify and determine the role of centromere specific proteins and of centromere specific DNA sequences in centromere structure and function. We have identified two polypeptides that appear to be uniquely associated with the interphase persistent centromere: Cen(17) and STOP(145). Cen(17) is a histone- like protein associated with nucleosome core particles. We propose to use immune-electron microscopic procedures, immunofluorescence, in vitro biochemistry and molecular genetic approaches (particularly cDNA cloning and sequencing procedures) to study the fine structure of Cen(17) distribution, the nature of its packing in nucleosomes, the nature of its association with sub-nuclear structure, its sequence homology with known histones, and the sequence of DNA that it might specifically recognize in the centromeric region. STOP(145) is a well characterized microtubule associated protein. We intend to use approaches similar to those outlined for Cen(17) to analyse STOP(145) as a centromeric protein. Further, we wish to determine if STOP(145) interacts directly with Cen(17) in the centromere. Since the centromere links chromatin to microtubules in the mitotic spindle, our identification of two centromeric components (one of which appears to link to nucleosomes, and the other of which binds to microtubules) is a promising beginning to understanding the molecular nature of this organelle's function. The centromere is of critical importance to the accurate inheritance of the genome. The project's health relatedness is therefore fundamental. Understanding of centromere function can unravel the molecular events involved in the induction of chromosome anomalies; in tumorigenesis, in non-disjunctional disorders, in acute myelogenous leukemia, and in Robert's Syndrome.